Output control for amplifier systems



April 1939- A. J. 'STIMSON 2,155,807

OUTPUT CONTROL FOR AMPLIFIER SYSTEMS Filed June 16, 1936 2 SheeRs-Sheet 1 BI'BHTTERY HIM-H Zlfiiinson Inventor Attorney Ap 1939. A. J. STIMSON 2,155,807

OUTPUT CONTROL FOR AMPLIFIER SYSTEMS Filed June 16, 1936 2 Sheets-Sheet 2 AMPL/F/fl? ii- EI M141. .3mm

v Inventor A [for ne y Patented 4 1 25,

T OFFICE,

ou'rru'r coN'rnoL roa mums SYSTEMS Arthur J. Stimson, Spokane, want, assignor to Spokane Casket Company, Spokane, Wash.

Application June 16, 1936, Serial No. 85,473 v 8 Clalml.- (Cl. 179-1) Y My present invention relates to sound equipment which uses an electron tube amplifier and more particularly to an output control for amplifier systems.

There are many conditions under which sound equipment is used'such as public address systems, electro-magnetic phonograph reproductions, and in the sound motion picture field where it is very desirable to have the microphone needle 10 and photocell noises and exciter lamp hum reduced to a point-where they will be inaudible during the period when no signal is being reproduced, or during the silent periods of an amplifier system. Normally, when an amplifier is being used a condition is present where the original signal must be appreciably amplified in order to be of useabl strength. Naturally, all background noises are likewise amplified. 'This is particularly true in public address work, in electrical reproduction of phonograph records and in sound pictures where areasonably high gain is required of the amplifier. This gain'can easily reach proportions where the scratch of a phonograph needle increases to a degree of audibility 25 that is not only very undesirable, but positively identifies the sound output as originating on a record.

The principal object'of my present invention is, therefore, to provide a control means for the output of an amplifier system that will reduce the amplifier output, during a period where no signal is impressed, to such a low intensity that there will be no audible output.

A further object of my invention is to provide 35 means to cause the immediate functioning of the amplifier system, upon application of input voltage exceeding a given minimum value, and immediate stopping of the output when a given minimum of input voltage obtains.

40 A further object is the provision of means to cause immediate functioning of the amplifier system, upon application of input voltage exceeding a given minimum value, and a gradual decrease of output when a given minimum of input voltage 45 obtains.

A further object is the provision of means to cause a gradual increase in' output up to the operating level of the amplifier system, upon application of input voltage exceeding a given mini- 50 mum value and a gradual decrease of output when a given minimum of input voltage obtains. v

A further object is the provision of means for limiting the low level to which the output of the amplifier shall fall when a given minimum of 55 input voltage obtains.

Other and more specific objects will be-apparent from the following description taken in connection with the accompanying drawings, where- Figure 1 'is a diagrammatic view of a circuit I using my invention, in a simplified form, wherein the field supply rectifying tube itself is. actuated by a variable resistor.

Figure 2 is a diagrammatic circuit, somewhat similar to Figure 1, showing my control means 10 as being applied to a complete amplifier unit wherein the actual field supply rectifier circuit is not altered, but another diode is used as a variable resistor. I

Referring to Figure 1 of the drawings, numerals 6 and 5 designate, respectively, the input and output tubes of a conventional amplifier. These may be of any suitable type normally used in such positions.v As acontrol tube 6 I prefer to use a triode of the indirectly heated cathode type :0 as lending itself most suitably to my control arrangement. ,A suitable field supply rectifying tube 8 is used to supply the field current for the output device. In the illustration a dynamic type speaker I2 is shown. A coupling condenser ll is used for applying a portion of the signal voltage to the grid of control tube 6. The bias battery it connected to tube 6 is provided as a means of adjusting the platecurrent. The purpose of C battery i6 is for adjusting the plate current of- 3o tube 6 to zero when no signal is applied. A storage condenser I8 is used in conjunction with resistor 20 for controlling the relay coil 22 of relay 23. A variable resistor 24 is placed in the filament circuit of tube 8 to control the voltage which is applied to the filament upon the closing of the contacts of relay 23. For simplification, in this circuit, I have illustrated a B battery as 26, this of course might be any suitable type of plate supply. Transformers 21 and 28 provide, respectively, the filament supply and the plate supply for tube 8.

Referring to Figure 2 I have illustrated a simplified circuit arrangement coupled to a conventional amplifier 30 having the signal output terminals 32 and 33 and the field current supply terminals 34 and 35 which, in the illustration, energizes the field coil 36 of the dynamic speaker 38. The circuit is provided preferably with a triode of the indirectly heated cathode type which is used as a control tube 6' for this version of my system. As in the circuit shown in Figure l, I have provided a diode vacuum tube or its equivalent 8'. I further provide a storage condenser 40 which is used in conjunction with resistor 42 a5 to control the opening of relay 22' upon removal of signal voltage. A coupling condenser I4 is employed as in the former circuit for the application of signal voltage to the grid of tube 8'. 44 is a variabieresistor shunting the contact 4|; 48 in turn is a relay contact shunting tube 8'. A switch 48 is also connected in this shunt circuit. 48 is a relay'contact in the filament circuit of tube 8'. A switch'll is also providedto supply the necessary filament current. 1

Method of operation Assuming that the amplifier is connected to a proper supply source and in an operating condi- 3 tion; a signal is applied to the grid of the triode 4 of Figure 1. Due to the conventionalaction of a vacuum tube upon application of a voltage to the grid, plate current fiows through the inter-stage transformer, imposing an amplified version of the original signal upon the output tube 8, which in turn draws controlled plate current, inducing alternating current variations in the voice coil of speaker l2 through the output transformer. It is assumed that the filaments of rectifying tube 8 are cold due to the fact that the filament circuit is open through relay contacts 23. There is no field current, therefore, on speaker I12 and very little or 7 no motion of the speaker cone results from application of varying currents-to its voice coil.

However, upon application of signal to triode'4 and the consequent variation in plate current of that tube, a portion of the plate current variations are imposed upon the grid of the control tube 0 through the coupling condenser I4. Though the tube 8 has been biased with the C battery l8 at a cut-off point, the application of the signal voltage to the grid, allows plate current to fiow during positive half-cycles through the relay coil 22 to the plate of triode 8, to the cathode, and back to the B battery, completing the circuit. Jpon the fiow of current through the relay coil 22, the resultant magnetism of that coil draws the contacts 23 together closing the secondary circuit of transformer 21 and filaments of tube 8. .As the filament of tube 8 becomes heated a current constantly increasing to full strength flows from the transformer 28 to the anodes, through thespace of the tube to the cathode, then on to the field magnet and back to the center tap of transformer 28 thereby completing the circuit, and energizing the field Ill of speaker l2. Inasmuch as the magnetic strength of field III is gradually increased the audible output of speaker i2 is also gradually increased, thus producing the fade-in effect upon application of signal voltage to the amplifier. Upon removal of the signal voltage, tube 8 receiving no further signal voltage through coupling condenser i4 plate current ceases to fiow, the magnetic field of coil 22 collapses, and contacts 23 open. This opens the circuit of filament of tube 8 and as the filament cools, the current to the field coil gradually drops, and the resultant movement of the speaker cone or other output device and, consequently, the audible output is gradually reduced to a non-operative level, thus producing the "fade-out effect.

The variable resistor 24 which is placed in the filament circuit of tube 8 controls the voltage which is applied to the filament upon the closing of contacts 23. Inasmuch as a higher voltage produces a hot filament more rapidly, and heats it to a higher degree, the application of full voltage to the field i8 is more rapid, and due to the higher heat of the filament the cooling is slower,

and therefore, current flows through the field for a greater period of time after the filament circuit has been broken. fade-in with a slower fade-out. through the manipulation of resistor 24. a 1 i In the circuit shown in Figure 2, diode 8' is used as a variable resistor to control the ,fieldcurrent to 0011 88 of the output device. or speaker.

- Upon application of a signal voltage to the amplifier 88 and the resultant amplified version, at output terminals 22 and 38 to'voice coil of speaker 88. a portion of this output is applied to the grid of tube 8' through thecoupling condenser l4. Provision must be made to apply sumcient driving voltage to tube 8', from the voice coil of speaker 88.

Inasmuch as tube 8! is biased by means of 0 battery It to cut-off and no plate current is fiowing, relay coil 22' is'npt energized and contacts 48 and are, therefore, open. Upon application of signal voltage, plate current fiows through relay ycoil 22' to the plate and cathodeof tube 0'. This energizes coil 22', closing contacts 48 and 4|.

With switch 58 closed, the closingof contact 48 gradually heats the filament of tube and current fiows in proportion to its temperature from terminal 85 to the anode, to the filament, to field 8 8, and to terminal 84, thereby causing field It to become energized, and resulting in the movement of the voice coil of speaker 38, and producing an audible output. Inasmuch as the filament of tube 8' is heated gradually, and the field 28 becomes energized in the same manner, the audible output of speaker "is gradually built up to full .strength, producing a "fade-in eifect. Upon removal of signal voltage to the amplifier, and, consequently, to the grid of triode 8', plate current ceases to flow through tube 8 and relay coil 22', and contacts 48 and 45 open, the filament of tube 8' cools gradually producinga gradual drop of! in the audible output of speaker 28; this constitutes the fade-out" effect. v

Relay contact 45 is connected across tube8' by switch 46. When this switch is closed, upon application ofa signal to the grid of tube 8' and the resultant closing of contact 45, full field voltage is applied to field 28 and full audible output of speaker 28 is attained. Upon removal of the signal voltage, however, and the consequent opening of contact 45 the field does not collapse immediately, but is reduced in proportion to the cooling of filament 8, thereby producing the instant "cut-in and "fade-out effect. It is assumed that switch 58 has been closed.

Were switch 50 to be open, the filament of tube 8' would not become heated upon closing of contact 48, and upon removal of the signal voltage This produces a more rapid.

from the grid of tube It, and the consequent opening of contact, 45 would cause the speaker field to immediately collapse and the audible output would cut off instantly, thus producing the cut-in" and cut-out effect.

Resistor 24' controls the rate of heating and cooling of the filament of tube 8, as in the case of the circuit of Figure 1.

Upon removal of signal voltage, resistor 44, of Figure 2, shunts contact 45 as well as tube 4' when switch 46 is closed, thus controlling the minimum value of field current and consequent audible output at which speaker 38 will operate. Were resistor 44 to be reduced to zero the entire noise eliminating system would be rendered inoperative,

The foregoing description and'the accompanying drawings are believed to clearly disclose a preferred embodiment of my invention but it,

will be understood that this disclosure is merely illustrative and that such changes in the invention may be made as are fairly within the scope and spirit of the following claims:

I claim:

1. In an amplifier system including a reproducing output device and a thermionic rectifier for supplying the output device with field excitation, a control means comprising a thermionic tube adjusted so that a signal applied to said tube will cause a change in the average plate current of said tube, a relay connected in the plate circuit of said tube, a pair of contacts on said relay, these contacts controlling the flow of filament current to the thermionic rectifier tube which supplies field excitation to the output device and a rheostat to control the magnitude of the filament current in said rectifier.

2. In an amplifier system including a reproducing output device and means for supplying field excitation to the output service, a control means comprising a thermionic tube adjusted so that a signal applied to said tube will cause a change in the average plate current of said tube, a relay connected in the plate circuit of said tube, a multiplicity of contacts on said relay, a thermionic diode whose filament temperature regulates the field excitation of the output device, the flow of filament current in said diode being controlled by one pair of contacts on the relay, while a second pair of contacts on the relay shunts the diode, a switch in series with each pair of relay contacts to render the same inoperative at will, a rheostat to control the magnitude of the filament current in the diode and an adjustable resistor shunted across'the diode to regulate the minimum value of field excitation.

3. In an amplifier system including a reproducing output device and a thermionic rectifier for supplying the output device with field excitation, a control means consisting of a relaying device, said device connected so that the application of a signal will initiate the fiow of filament current to the thermionic rectifier tube which supplies field excitation to the output device, and a rheostat to control the magnitude of the filament current in said rectifier.

4. In an amplifier system including a reproducing output device, a control means consisting of a relaying device, a thermionic tube whose filament temperature regulates the field excitation of the output device, said relaying device enabling an applied signal to control the flow of filament current in said thermionic tube, and a rheostat to control the magnitude of the filament current.

5. In an amplifier system, a control means comprising a thermionic tube adjusted so that a signal applied to said tube will cause a change in the average plate current of said tube, a relay connected'in the plate circuit of said tube, a plurality of contacts on said relay, a thermionic rectifier having its filament current controlled by contacts on said relay, an output device requiring field current which is controlled by the filament temperature of said thermionic rectifier.

6. In an amplifier system a control means comprising a thermionic tube adjusted so that a signal applied to said tube will cause a change in the average plate current of said tube, a relay connected in the plate circuit of said tube, a plurality of contacts on said relay, a source of electric current controlled by contacts on said relay, elements having an electrical-time lag being incorporated in said source of electric current, an output device requiring electric current for field excitation, said output device having its field terminals conductively coupled to the aforemen- I tioned source of electric current, electric current from said source to field terminals being regu lated by said elements" having an electrical-time lag.

7. In a system for amplifying and reproducing audio frequency electrical energy, a method of controlling the amount or degree of reproduction wherein a portion of said audio frequency electrical energy is converted to direct current energy which is approximately proportional to the average value of the audio frequency electrical energy, said direct current energy controlling the rectification of a considerably larger value of alternating current energy not associated with the aforementioned audio frequency electrical energy, said rectified alternating current energy being necessary in the reproduction of the desired audio frequency energy.

8. In an electrical system for receiving amplifying and reproducing audio frequency energy, a method of controlling reproduction of the audio frequency energy wherein a rectified portion of the audio frequency energy initiates the flow of direct current energy necessary to effect reproduction, said fiow of direct current energy being subject to an adjustable electrical time lag.

ARTHUR J. STIMSON. 

